1. Field of the Invention
This invention relates to molding resins and more particularly it relates to blends of alpha-olefin/unsaturated carboxylic acid ionomers and linear polyesters.
2. Description of the Prior Art
Copolymers of ethylene (E) and methacrylic acid (MAA) partially neutralized with sodium or zinc ion (ethylene ionomers) are tough, abrasion resistant molding resins with excellent impact resistance and good tensile properties. An important deficiency is their lack of heat resistance, indicated by a heat deflection temperature (HDT) of 40.degree.-45.degree. C.
Polyethylene terephthalate (PET) is used as a molding resin for producing structures exhibiting improved heat resistance (HDT of unannealed PET=72.degree. C.), high flexural modulus but with poor impact resistance as shown by notched Izod impact values (unannealed PET) of 0.4-0.5 ft-lb/in. at 23.degree. C.
U.S. Pat. No. 3,435,093 discloses blends of polyethylene terephthalate (PET) and alpha-olefin/alpha,beta-unsaturated carboxylic acid copolymers wherein the carboxylic acid groups are 0-100% neutralized by metal cations. A surprising improvement in toughness is taught for these blends, along with less mold shrinkage and water uptake. Izod impact values of blends indicated in the Examples of this patent range from 0.52 to 1.12 compared to a value of 0.26 for 100% polyethylene terephthalate. The weight of the ethylene/methacrylic acid copolymer is disclosed to be about 5-150% of that of the polyethylene terephthalate, i.e., 4.75-60% ionomer and 40-95.25% PET. The preferred composition is disclosed to be 5-45% ionomer based on the weight of PET, while the optimum composition is disclosed to be one wherein the ethylene methacrylic acid copolymer is about 25% of that of polyethylene terephthalate. Preferred cations taught for the neutralization of the carboxylic acid groups are sodium, potassium, calcium, magnesium, zinc, and lead.
U.S. Pat. No. 3,639,527 discloses polyester/ionic copolymer thermoplastic molding compositions wherein the ionic copolymer is present to the extent of 0.01 to 25% of the weight of the blend. The surprising feature of that invention is stated to be that "by the addition of ionic copolymers to the polyester moulding compositions are obtained which during processing crystallize very rapidly in the mould to furnish mouldings having a very good dimensional stability, without impairing the hardness and abrasion resistance. It was also surprising that the impact strength of the polyesters modified in this manner is increased".